The present invention relates to a microwave plasma processing apparatus, and especially to a microwave plasma processing apparatus for thin film formation, etching, sputtering and plasma oxidation on the surface of processing objects by utilizing high density plasma generated with electron cyclotron resonance.
A conventional microwave plasma processing apparatus utilizing electron cyclotron resonance is disclosed, for instance, in JP-A-64-64221 (1989).
Referring to FIG. 1, the microwave plasma processing apparatus will be explained.
As FIG. 1 reveals, the microwave plasma processing apparatus 30 is provided with the microwave guide 40 which transmits a microwave from a microwave oscillator (not shown in the figure) in the direction indicated by the arrow 31, the vacuum vessel 39 into which the microwave 31 from the microwave guide 40 is supplied into interior through the microwave inlet window 41 and plasma processing is performed to the processing object 34 by supplying necessary gases from the gas inlets 32, 33 and generating plasma of the gases 42, the magnetic field generation coils 36, 37 which are arranged at an outer periphery of the microwave guide 40 and the vacuum vessel 39 and generate a magnetic field, and a gas outlet 38 which is formed at the side of the vacuum vessel 39 and connected to an evacuation apparatus for reducing an interior pressure of the vessel to a desired reduced pressure.
Next, operation of the microwave plasma processing apparatus will be explained.
The microwave plasma processing apparatus utilizes electron cyclotron motion which is generated by charging a magnetic field to a plasma. That is, when a magnetic field having a magnetic flux density which makes a cyclotron frequency of an electron coincide with a frequency of the microwave 31 from the microwave guide 40 is charged to the plasma by the magnetic field generation coils 36, 37, the resonance of the cyclotron motion of the electron and the microwave occurs, and consequently, a high density plasma is obtained. By utilizing the high density plasma, such processing as formation of a thin film on the surface of the processing object 34, etc., is performed.
When performing the processing, necessary gases 42 are supplied through the gas inlets 32, 33 in the direction indicated by the arrows as previously described. And, the vacuum vessel 39 is evacuated by the evacuation apparatus (not shown in the figure) such as a vacuum pump, etc., through gas outlet 38 which is provided at the side of the vacuum vessel 39 for maintaining the interior at a desired reduced pressure.
But, with the previously described conventional microwave plasma processing apparatus 30, sufficient evacuating speed is not obtainable when the apparatus uses a large amount of reaction gas because the gas outlet 38 is provided between the two magnetic field generation coils 36, 37 which are separated in the direction along the microwave transmittance at the outer periphery of the vacuum vessel 39.
For instance, the previously described microwave plasma processing apparatus 30 has the evacuation characteristics of reaction pressure of 1.times.10.sup.-3 Torr. When using a silicon wafer of 100 mm diameter as, the processing object 34 and the reaction gas is supplied at 100 ml/min. and assuming a vacuum pump having an evacuating speed of 1800 l/sec as an ordinary vacuum pump, the evacuating conductance of the apparatus is about 4300 l/sec. Further, taking a case of supplying the reaction gas by 500 ml/min. in order to process larger objects for an example, although assuming that the reaction pressure is 3.times.10.sup.'1 Torr, the evacuating conductance of the apparatus of about 5100 l/sec with two of the above described vacuum pumps becomes necessary and, consequently, a plurality of vacuum pumps for the microwave plasma processing apparatus 30.
As previously explained, the conventional microwave plasma processing apparatus 30 has a problem that a plurality of vacuum pumps are necessary in order to process large size processing objects because the evacuating speed was not sufficient in the case of the processing with supplying a large amount of the reaction gas.